This invention relates in part to metal hydrides and complex hydrides that may be used to form a stable hydrogen capacity for hydrogen cycling. There remains a need for improvements in metal and complex hydrides with respect to hydrogen storage capacity, dehydriding temperatures, and reversibility of the hydrogen sorption and desorption cycles. For instance, it is known in the art as set forth in U.S. Pat. No. 7,094,387 directed to molten state processes of forming unique metal hydrides and complex metal hydrides. However, there remains room for improvement and variation in the art directed to techniques and resulting materials to form stabilized high capacity complex hydrides.
Currently hydrogen is stored on board a vehicle under 5,000 to 10,000 psi pressure. However, these storage systems are not efficient from a volumetric point of view. For example, the storage density of hydrogen gas at 10,000 psi is only 0.035 g/cm3, which is approximately half the storage density of liquid hydrogen at the 20K boiling point of hydrogen. Despite the higher storage density, liquid hydrogen is an undesirable storage form due to hydrogen liquefaction storage loss and short lived dormancy at 20K due to boil off.
Complex metal hydrides, such as alanates (e.g., LiAlH4, NaAlH4 and KAlH4) and borohydrides (e.g., LiBH4, NaBH4 and KBH4), show promise as materials for solid state storage of hydrogen. For example, the theoretical hydrogen volumetric storage density in lithium borohydride (LiBH4) is approximately 0.12 g/cm3, more than three times the density of gaseous hydrogen at 10,000 psi.
However, many complex metal hydrides are unsuitable for hydrogen storage applications. For example, Al(BH4)3 is an unstable compound, and its vapor ignites spontaneously on exposure to air containing only traces of moisture.
A great deal of research is currently underway with other complex hydride compounds and materials to determine the most efficient and useful hydrogen storage material.
There is a need for solid state hydrogen storage materials having improved chemical stability, stable hydrogen capacity with cycling, and enhanced kinetics compatible with automotive and other portable power source requirements.